JPS5832811B2 - hybrid circuit device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an active hybrid circuit arrangement for communication systems, particularly time division multiplexed (TDM) communication systems.

The art has advanced to the extent that active electronic hybrid circuits can be utilized to provide bidirectional transmission over communication lines via separate unidirectional transmit and receive channels of a common time division transmission path.

An example of such an electronic hybrid is U.S. Pat.
No. 154 or US Pat. No. 3,828,146.

Q) Each hybrid circuit includes an operational amplifier for transmitting the bidirectional station line transmit and receive signals to the unidirectional TDM transmit and receive bus and a capacitor arrangement for TDM signal sampling and holding.

Feedback is provided between the aforementioned operational amplifiers to control signal cancellation to prevent unwanted reflow of transmitted and received signals within the device.

The extent of such signal cancellation depends essentially on delicate impedance balances, such as the station line impedance at the operating frequency and circuit element parameters.

Maintaining impedance balance has proven problematic in the past, and today's customers therefore require active hybrid stability and transmission quality over the operating frequency range.

Such unbalance and instability can damage transmission fidelity,
It increases system sensitivity to unwanted crosstalk, noise transients, and ringing conditions.

In view of the foregoing, there is a need for means to improve impedance balance and stability in active hybrid circuits, and in particular to minimize crosstalk, ringing, and high noise transients in active hybrid circuit operation used with telephone lines of TDM equipment. It is clear that there is a need to achieve quality transmission, and it is an object of the present invention to meet that need.

The hybrid included in the active/hybrid device according to the invention provides a single path for two-way communication on the telephone line;
It provides unidirectional transmission for separate transmit and receive TDM buses.

Transmit and receive operational amplifiers within the hybrid are used to achieve hybrid balance and signal cancellation.

Each amplifier has an inverting and a non-inverting input as well as a single output.

A resistor connected between the amplifier output and the inverting input provides feedback for cancellation of the transmitted and received signals appearing at the non-inverting input.

Signal cancellation prevents signals transmitted from the telephone line from being routed back (i.e., reflowed) through the TDM transmit channel, TDM system, and hybrid receive amplifier to the transmitting telephone line and hybrid transmit amplifier. It is necessary to

Similarly, signal cancellation is necessary to prevent signals received on the telephone line via the hybrid from undesirably reflowing via the hybrid transmit amplifier to the TDM bus.

Without such signal cancellation and hybrid balance, echoes or low frequency ringing (rain barrel effect or sinusoidal effect) will occur.

The active hybrid device according to the invention also includes an interface circuit that connects the telephone line to
- Contains a line transformer with high magnetization to couple to the hybrid.

The circuit arrangement on the first winding side of the transformer includes a line relay, a feed inductor and a DC (direct current) blocking capacitor (first capacitor).

The secondary winding side of the transformer is connected in series with a low frequency equalizing capacitor (second capacitor) for reducing the DC current flowing through the transformer and for low frequency feedback to the transmitting amplifier as described below. has been done.

The present invention is directed to the problem of mismatch in hybrid circuits due to the resonant impedance caused at low frequencies by the DC blocking capacitor of the interface circuit and the inductance of the transformer. The connection to the inverting input of the hybrid is provided by a resistive feedback path, increasing the low frequency response of the hybrid.

At low frequencies, the impedance of the equalizing capacitor is relatively high, so the voltage appearing will be higher than at high frequencies.

Therefore, by connecting the capacitor voltage to the inverting input of the hybrid transmitting amplifier at low frequencies, the feedback resistor cancels the low frequency resonant voltage caused by the undesired aforementioned resonance applied to the non-inverting input of the transmitting amplifier, and the transmitting amplifier serves as a negative feedback.

This device thus improves the low frequency transmission of TDM mechanisms6.
The example interface circuit further provides a DC
Includes a resistor-capacitor network to control unbalance.

The details of the present invention will be explained below with reference to the embodiments shown in the figures.

The figure shows an active hybrid device according to the invention.

Transmission (summation) shared in TDM function by all line circuits and other functional circuits (not shown) of the device
A plurality of two-wire telephone lines TL1-TLn and each line circuit L C1 are connected to the busbar (TB) and the reception (distribution) busbar (RB).
A plurality of telephones T, -Tn are shown coupled via -LCn.

The configuration of each line circuit is essentially the same.

Therefore, the line circuit LC. Only the details will be shown and explained.

Line circuit LC. contains two basic components.

That is, the active hybrid AH1 and the interface circuit IC between the hybrid and the telephone line T Ll
, is.

Interface circuit IC1 provides a drive voltage of -48 volts and ground potential to telephone TL1 via tip and ring conductors 1 and 2 of line TL1, windings 3 and 4 of inductor 50, and windings 6 and 7 of line relay 8. supply

The windings 3 and 4 of the inductor 5 provide a path of low resistance for direct current and relatively high impedance for frequencies above several hertz.

A capacitor 9 is connected in series with the line transformer 110 primary winding to the ring conductor 2 and tip conductor 1 to block the DC voltage applied to the telephone T1 so that no DC current flows through 110.

This is because the flow of such a direct current, even at very low levels, through the transformer windings can cause core saturation, leading to an undesirable reduction in communication quality.

The transformer 11 also serves to protect the electronic components of the hybrid AH1 from disturbances often encountered in the tip and ring conductors, such as lighting shocks and short circuits in power lines, as well as direct current or low-frequency high voltages.

As a feature of the invention, the transformer 110 secondary winding 12 has a terminal 13 connected to a low frequency equalization capacitor 14 to provide a low impedance path to ground at frequencies above approximately 300 Hertz.

At lower frequencies, capacitor 14, along with negative feedback resistor 15, which controls the gain of hybrid transmit amplifier 21, as explained below, serves to improve low frequency transmission and reduce hybrid unbalance in accordance with the present invention.

In an embodiment of the invention, a p-wave circuit including an inductor 16 and a capacitor 11 couples the terminal 18 of the secondary winding 12 to the hybrid AH1 via an impedance matching resistor 19 and a voltage dividing resistor 20.

The p-wave network serves two important functions.

namely, attenuating out-of-band power entering line TL1 to prevent aliasing, and attenuating out-of-band modulation products of the output signal from line TL.

The hybrid AH samples communication signals from the unidirectional transmission bus TB and reception bus RB, which are separated under TDM exchange control, via an interface circuit.
Storage and transmission are provided to bidirectional transmission line TL1.

The hybrid AH includes transmit and receive operational amplifiers 21 and 22, gain control resistors 23-26 between the amplifiers, a sample and hold capacitor 27, a sample and hold compensation capacitor 28, and a transmit pulse current supply capacitor 29 and resistor 30.

Amplifiers 21 and 22 have a flat response to voice side wavenumbers and include inverting and non-inverting inputs.

Resistors 2.3 and 24, like resistors 25 and 26, respectively maintain hybrid balance and set the inverting and non-inverting gains of amplifiers 21 and 22 to maintain the desired transmission level.

Before further describing the gain adjustment mechanism of a typical embodiment, it is important to note that in order to achieve high quality transmission characteristics, the transformer 11 exhibits a very large magnetic inductance at low frequencies, e.g., 7 Henrys at 30 Hz. I would like to mention that you should use .

On the other hand, it has been found that such a high magnetic inductance coupled with capacitor 9 produces parallel resonances at low frequencies.

As a result, this parallel resonance causes the hybrid AH to become unbalanced, which causes stability problems or instability in TDM communications.

This instability is due to a mismatch in the cancellation, allowing a voltage greater than that required for proper cancellation to be fed back through resistor 20 to no-brid transmit amplifier 21.

In accordance with the present invention, this instability problem has been solved by providing a negative feedback compensation resistor 15 working in conjunction with capacitor 14.

Resistor 15 controls the gain of the inverting input of amplifier 210 from low frequency to high frequency, and at the same time controls the gain of amplifier 210 at low frequency.
It controls the magnitude of the signal fed back from the capacitor 14 to the inverting input.

When the impedance of capacitor 14 is relatively large at low frequencies, resistor 15 returns a larger signal from capacitor 14 to the inverting input of amplifier 210 than at high frequencies, thereby increasing the overall gain for the signal at the non-inverting input of amplifier 21. I'm trying to reduce it.

Resistors 31 and 32 correct for the DC unbalance created by resistor 15 to the series connection of capacitor 14 and winding 12 and thence through inductor 16 and resistor 20 to the non-inverting input of transmit amplifier 21. included as a voltage divider.

The capacitor 33 prevents the influence of the resistor 32 from occurring at frequencies of 10 hertz or higher, for example.

Capacitor 14. ! It is desirable that the value =33 be selected so that the influence of the DC balancing element 32 disappears before the frequency increases and the impedance of the capacitor 14 becomes small.

A resistor 19 in series with the output of the receiving amplifier 22 is an interface circuit C1 for realizing hybrid balance.
Provides impedance matching for the telephone line TL and the effective impedance termination of the telephone T1 - an hybrid matching resistor.

The value of resistor 19 is typically chosen to maximize the attenuation of reflections due to reflow.

The line circuit LC1 has the output of the transmitting amplifier 21 and the non-inverting input of the receiving amplifier 22 simultaneously connected to the PAM distribution circuit 36 during time slots of the TDM frame assigned by the TDM controller (not shown). Time division switches 34 and 35 are provided for connecting to each connected transmit and receive bus TB and RB.

At the output of amplifier 21, resistor 30 and capacitor 29
is provided.

These are connected to the transmitting resistor 3 at the moment the switch 34 is closed.
1 to the transmission bus TB and for producing a pulsed current for sampling the signal to be transmitted from the line TL1 via the amplifier 21 due to the initial disabled state of the amplifier 21. It is something.

Capacitor 29 is connected to resistor 30 for protection against noise and crosstalk through the power source and in particular to provide sufficient damping to prevent TDM pulse sampling transients from creating high noise crosstalk transients in the system. are connected in series.

The PAM distribution circuit 36, which is known in the prior art, handles the TDM time signal appearing on the transmission (summation) bus TB.
Collecting all of the signal sample pulses in the slots and supplying them to the receive (distribution) bus RB via a simultaneously closed switch, eg switch 35, for application to a respective sample/hold capacitor, eg capacitor 27.

To further improve transmission quality, a resistor 38 is connected across capacitor 21 to limit undesirable voltages that may develop on capacitor 27 due to leakage current in switch 35 and bias bias in amplifier 22.

The capacitor 27 stores the sample signal applied to the receive bus RB for the entire TDM sampling frame period, and such storage allows the reconstruction of the sample waveform into a stepped signal in a known manner. Achieved.

The hybrid AH further includes a capacitor 28 connected between switches 34 and 35 on its amplifier side;
This forms a capacitive divider with capacitor 27 to maintain the desired hybrid balance throughout the sample frame and not just at the time slot signal sampling instant.

In the embodiment of the present invention shown in the figure, in order to increase the stability margin of the hybrid, the non-inverting input of the transmitting amplifier 21 and the receiving amplifier 2 are connected to each other.
A filter consisting of an inductor 16 and a capacitor 17 is provided between the junction with the output of the transformer 110 and the secondary winding of the transformer 110.

Capacitor 17 is connected to transformer 110 secondary winding and capacitor 1
There is a parallel relationship with 4.

This inductor capacitor filter has a frequency nfs
2 (fs is the TDM sampling frequency, n is an odd number).

). Without this filter, imbalances in the hybrid at relatively high frequencies often result in TDM oscillations at -.

This high-frequency hybrid imbalance is caused by two phenomena in principle.

First, the receive amplifier 22 tends to be unbalanced at high frequencies due to the high frequency attenuation of the sample/hold capacitor 27 at the non-inverting input versus the inverting input.

Second, the impedance of the transformer and the terminal impedance of the tip and ring leads 1 and 2 tend to increase significantly at frequencies above fs/2.

Although this filter consisting of the inductor 16 and the capacitor 1 improves unbalance at high frequencies, it has been found that doing so causes attenuation in the high frequency portion of the audio band, resulting in deterioration of transmission quality.

In order to relieve this attenuation, and at the same time, the receiving amplifier 22
In order to improve the degree of mismatch at
20 by a resistor 39 and capacitor 40 connected to the inverting input.

Hybrid AH1 is connected to telephone line TL via inductor 16.
, and separate transmit and receive buses TB and RB are used for TDM communication.

It is therefore important that the transmitted signal returns to the shared bus via the receive amplifier 22 and through the inductor 16; likewise, the received signal does not return to the transmit bus.

Hybrid AH1 requires equilibrium to achieve this function.

During transmission by telephone T1, it is considered balanced if no transmitted signal power is received in the input direction at tip and ring conductors 1 and 2.

This is due in part to the matching termination impedances of the transmit and receive buses TB and RB, the matching impedance of resistor 19 to the termination impedance to telephone T1, and to cancel the transmitted signal on the receive bus appearing at the output of amplifier 22. This is realized by performing feedback from the transmission amplifier 21 through the resistor 25 to the inverting input of the amplifier 220.

The hybrid AH1 also receives signals from the telephone T1/other line circuits from the reception bus RB, and also sends signals from the telephone T1/other line circuits to the amplifier 2.
Equilibrium is considered when the received signal power at the output of 2 does not return to the transmission bus TB.

This is due in part to the aforementioned matching conditions and to the resistor 2 from the output of receive amplifier 22 which cancels out the received signal at the non-inverting input of amplifier 21 appearing at its output.
4 to the inverting input of amplifier 210.

...Ibrid AH, in equilibrium, enables two-way audio frequency communication on line TL1 as follows:
It functions to allow separate unidirectional TDM communications on the transmit and receive buses.

As an example, assuming that the voltage Vr of the received signal is stored in the sample/hold capacitor 27, the voltage Vr
appears at the input and output of amplifier 22.

Since the tip and conductors 1 and 2 are terminated by the impedance of the telephone T1 equal to the impedance of the matching resistor 19, a voltage +Vr appears at the inverting input of the r amplifier 210 and - appears at the input power of the amplifier 21.

These signal voltages are therefore combined by amplifier 21, correspondingly producing zero received signal voltage at the output of amplifier 21.

For transmission in the opposite direction, ie from the telephone Ti, assuming that a voltage Vs is present across the tip and ring conductors 1 and 2, this appears as - at the voltage of the transmitter amplifier 21.

Furthermore, assuming that the output of amplifier 22 is in a balanced state and at zero potential, a voltage Vs appears at the output of amplifier 21.

The voltage Vs is summed and presented to the amplifier 22 during the assigned time slot through the PAM distribution circuit 36.

Voltage Vs therefore appears in both the positive and negative forces of amplifier 22 and cancels, resulting in a zero transmit voltage at the output of amplifier 22, in accordance with the assumptions made above.

For example, the following resistor, capacitor, and inductor element values are suitable for use in the example line circuit.

It is understood that the apparatus described above is an example of the application of the principles of the present invention.

From this description, it is clear that numerous other arrangements can be devised by those skilled in the art without departing from the scope of the inventive concept.

[Brief explanation of drawings]

The figure is a circuit diagram showing an embodiment of the hybrid circuit device of the present invention. [Explanation of symbols of main parts], Interface circuit...
...I C, = I Cn, hybrid circuit -
...AH, =AHn, transformer...11.
First capacitor...9, Second capacitor...
...14, Connected circuit ...15゜

Claims (1)

[Claims] 1. A hybrid circuit device for interconnecting a bidirectional transmission line to a receiving transmission line and a transmitting transmission line, comprising: a transmitting amplifier each having two inputs and one output; a receive amplifier, where the output of the transmit amplifier is connected to the transmit line for transmitting communication signals to the transmit line, and one input of the receive amplifier is connected to the receive line; a feedback circuit connected to connect the output of the transmitting amplifier to the other input of the receiving amplifier and connecting the output of the receiving amplifier to one input of the transmitting amplifier;
A secondary winding is connected to the bidirectional transmission line, and one end of the secondary winding is connected to the other input of the transmitting amplifier and the output of the receiving amplifier via a matching impedance, and the other end of the secondary winding is connected to the other input of the transmitting amplifier and the output of the receiving amplifier via a matching impedance. and an interface circuit consisting of a transformer connected to earth potential; a first capacitor (for example 9) connected, a second capacitor (for example 14) inserted between the other end of the secondary winding and ground potential, and a feedback signal to the transmission amplifier. a circuit (e.g. 15) interconnecting the junction of the two-conductor winding and the second capacitor to the one input of the transmission amplifier so as to Device. 2. A hybrid circuit device for interconnecting a bidirectional transmission line with a receiving transmission line and a transmitting transmission line, comprising a transmitting amplifier and a receiving amplifier each having two inputs and one output. An output of the transmitting amplifier is connected to the transmitting transmission line for transmitting a communication signal to the transmitting transmission line, and one input of the receiving amplifier is connected to the receiving transmission line. a feedback circuit connecting the output of the receiver amplifier to the other input of the receiver amplifier and the output of the receiver amplifier to the one input of the transmitter amplifier;
A secondary winding is connected to the bidirectional transmission line, and one end of the secondary winding is connected to the other input of the transmitting amplifier and the output of the receiving amplifier via a matching impedance. an interface circuit comprising a transformer, the end of which is connected to earth potential; the interface circuit is connected to the bidirectional transmission line in series connection with the primary winding of the transformer a capacitor (for example 9), a second capacitor (for example 14) inserted between the other end of the secondary winding and the ground potential;
, and a circuit (e.g.
5) In a hybrid circuit device consisting of: a parallel circuit of a resistor (e.g. 32) and a capacitor (e.g. 33) whose one end is connected to the ground potential, and a resistor (e.g. 31) connected in series at the other end; further comprising a circuit, wherein the bias circuit is connected to the other input of the transmitting amplifier to correct a DC imbalance caused by the interconnecting circuit (e.g. 15). Device.